Textured Perovskite Tandem Solar Cells

Halide perovskites exhibit many ideal properties for photovoltaics, as highlighted by the fact that lead halide solar cells (SCs) have now reached efficiencies >25%, a value close the theoretical limit of single-junction SCs.

A strategy to overcome this limitation is to combine two SCs, e.g. two perovskites of different compositions, into a tandem device to reduce thermalization and incomplete absorption losses. To maximize power output, each sub-cell must generate a maximum photocurrent matching that of the other sub-cell.

This can be achieved by a. careful optimization of the perovskites thicknesses, b. minimizing parasitic absorption in transport layers and electrodes, and c. depositing the SCs on textured substrates. Textures are employed by some SC technologies, e.g. silicon, to enhance absorption and reduce reflection losses.

Still, the use of textures in perovskite-based devices has been extremely challenging.

Record perovskite-based single-junction and tandem devices rely on solution-processing (spin-coating), complicating and often preventing the uniform coverage of textured surfaces, in addition to hindering their deployment on industry-relevant sizes.

This proposal aims to tackle both challenges by producing 30% perovskite-perovskite tandems, where all the functional layers (incl. perovskites) are grown conformally on textured substrates with high uniformity.

To track and improve the optoelectronic quality of the perovskites when developing new processing routes, a combination of three in-situ optical spectroscopies (Absorption, PL & Raman) will be implemented.

The methods will offer direct insights into the (trans-)formation of perovskites and emergence of defects or unwanted phases.

With the means to monitor the quality of the perovskites, the optoelectronic quality of narrow- and wide-bandgap perovskites will be improved through process and additive engineering to finally yield highly efficient textured perovskite-perovskite tandems.